The present invention relates to an improved disk drive that has an improved means for determining whether a correct data storage cartridge has been inserted into the disk drive and thereby protecting the disk drive against the insertion of incompatible or write protected disk cartridges in the drive. More particularly, the present invention relates to improved method and apparatus for determining whether a data storage cartridge that has a retroreflective marker has been inserted into the disk drive.
Removable disk cartridges for storing digital electronic information typically comprise an outer casing or shell that houses a rotatable recording medium, or disk, upon which electronic information can be stored. The cartridge shell often comprises upper and lower halves that are joined together to house the disk. The disk is mounted on a hub that rotates freely within the cartridge. When the cartridge is inserted into a disk drive, a spindle motor in the drive engages with the disk hub in order to rotate the disk within the cartridge. The outer shell of the cartridge typically has some form of opening near its forward edge to provide the recording heads of the drive with access to the recording surfaces of the disk. A shutter or door mechanism is often provided to cover the opening when the cartridge is not in use to prevent dust or other contaminants from entering the cartridge and settling on the recording surface of the disk.
As used in this application the term disk cartridge refers to any data storage device including tape drives.
Disk drives for receiving removable disk cartridges, including conventional 3.5" floppy disk drives, must have some mechanism for detecting the insertion or presence of a disk cartridge in the drive. The actuator that carries the recording heads of the disk drive across the recording surfaces of the disk should not be allowed to move unless the presence of a disk cartridge is detected. In the prior art, mechanical switches are typically employed to detect the presence of a disk cartridge within the drive. Such switches are typically positioned such that when a disk cartridge is inserted fully into the drive, the cartridge contacts the switch, thereby providing an indication that the disk cartridge is present.
When a data storage cartridge is inserted into a drive it is important that the type of cartridge be recognized by the drive as the correct type for safe and reliable use in that particular drive. Most removable cartridge drives (magnetic and optical) typically use approximately the same form factor cartridges, i.e., 3.5", 5.25", etc. Hence if one of these cartridges is inserted into the cartridge slot of the non-mating drive there is a large probability that either the drive (heads, load mechanism, electronics, etc.) or the data on the disk could be damaged.
Also, some cartridges are "write protected" by the user to prevent accidental erasure of important data by writing over it. It is important to protect against operation of the drive when an incorrect or write protected cartridge is inserted.
Retroreflective materials have been developed. This material has many periodic miniature corner cubes, or spherical elements, which reflect light striking it almost exactly upon its incident path. Retroreflective array materials are described in Jacobs, S. F., "Experiments with retrodirective arrays," Optical Engineering, Vol. 21, No. 2, March/April 1982; Rennilson, J., "Retroreflection--What is it and how is it used?" ASTM Standardization News, February 1982; and Venable, W. H., Stephenson, H. F. and Tersteiege, H., "Factor affecting the metrology of retroreflective materials," Applied Optics, Vol. 19, No. 8, April 15, 1980.
Recently issued U.S. Pat. No. 5,638,228 (the '228 patent), which issued on Jun. 10, 1997 is commonly assigned and has the same inventor, is hereby incorporated by reference. The '228 patent describes a disk cartridge that has a retroreflective material and a disk drive that has a light emitter and a light detector coupled to an electrical circuit that can be used to determine if the correct disk cartridge has been inserted into the disk drive. The emitter and detector determine if the correct data storage cartridge has been inserted into the disk drive by determining whether a data storage cartridge that has a retroreflector has been inserted into the disk drive. As described in the '228 patent, the magnitude of light reflected from a retroreflector to the detector will be greater than that reflected by a spectrol (mirror like) or diffuse deflector. Therefore, the detector can determine that a disk cartridge that has a retroreflective marker has been inserted into the disk drive when the magnitude of light received is above a predetermined threshold. Since the magnitude of light reflected from a spacial or diffuse reflector will not exceed the predetermined threshold, the detector will know that an improper data storage cartridge has been inserted when the magnitude of light received does not exceed the predetermined threshold.
By recognizing that the magnitude of light received is above a preset threshold limit, the detector knows that the light has been reflected by a retroreflector, and that the correct disk cartridge has been inserted into the disk drive. After recognizing this, the detector operates in conjunction with an electrical circuit to permit activation of the heads of the disk drive, so that the disk drive can interface with the disk cartridge is inserted into a disk drive, the detector will not see light emitted from a retroreflector. In this event, the detector and the electrical circuit will not enable the heads of the disk drive. This prevents the disk drive from operating.
While the emitter detector design disclosed in the '228 patent has proven to be effective for some disk drives, an improved design is needed, as disk drives become smaller and smaller in order to meet design constraints, in for example a lap top computer, the distance between the emitter detector pair and the retroreflective marker on a disk cartridge becomes smaller and smaller. Due to present design constraints, the distance between the emitter detector pair and the retroreflective marker on a disk cartridge has become so small, that the design disclosed in the '228 patent cannot be used to effectively distinguish between light reflected from a retroreflective surface and light reflected form other surfaces, such as a spacial or diffuse reflectors. At these small distances, the difference in the amount of light seen by the detector from the retroreflective marker and the amount of light seen from other sources becomes so small that it is difficult to distinguish between the sources. Consequently, the detector cannot effectively distinguish between light that has been reflected from other surfaces and light that has been reflected from a retroreflective marker.
This invention relates to an improved disk drive that has an improved emitter/detector that can be used to distinguish between light reflected from a retroreflective marker on a disk cartridge and light from other reflective sources. This improved emitter/detector can effectively distinguish between light reflected from a retroreflective marker and other reflective sources when the distance between the emitter/detector and the reflective material is relatively very small. This improved disk drive will also improve the ability to distinguish between light reflected from a retroreflective marker and light reflected from other sources, such as diffuse or specular surfaces, in disk drives having a relatively high distance between the marker and the detector.